Mechanical activation-enhanced doping and defect strategy to construct Fe–S co-doped carbon nitride for efficient photocatalytic tetracycline degradation and hydrogen evolution

Achieving a simultaneous increase in the redox performance of carbon nitride (CN) remains a challenge owing to the low utilization efficiency of photogenerated carriers. Herein, a novel "mechanical activation (MA)-enhanced doping and defect" strategy was proposed for structural modification of CN to enhance its performance. Specifically, CN, FeCl3, and thiourea were treated by MA to prepare a precursor with uniform dispersion and anchoring of Fe and S components in CN, and then the MA-treated precursor was calcinated to obtain a Fe–S co-doped CN composite (MA-Fe-S-CN) with abundant N vacancies. Under visible light illumination, MA-Fe-S-CN displayed outstanding photocatalytic performance for tetracycline (TC) removal (92.7%) and hydrogen evolution (2965 µmol g−1h−1) within 120 min, which was 3.3 and 4.1 times higher than those of CN, respectively. The superlative redox performance of MA-Fe-S-CN was attributed to that MA-enhanced Fe–S co-doping and N vacancies effectively modified the built-in electric field, electronic structure, and redox potential of CN. Experimental and theoretical analysis revealed that photogenerated electrons were trapped by N vacancies and directed to Fe active sites through efficient charge transfer channels (Fe–N and Fe–S), resulting in rapid charge transfer and effective separation and utilization of carriers. On this basis, possible mechanisms of photocatalytic TC degradation and hydrogen evolution were proposed. This work provides a green and economically feasible way for improving the redox performance of CN.